1. Field of the Invention
This invention relates to a light guide plate and an edge light backlight device containing the light guide plate, more particularly to a light guide plate and an edge light backlight device with superior local dimming effect.
2. Description of the Related Art
Currently, planar light units, cold cathode fluorescent lamps (CCFL), light-emitting diodes (LEDs), etc., are used as a light source for a backlight device of a liquid crystal display (LCD). With the raising concerns over environmental issues, LEDs with low energy consumption are widely used as a light source for LCDs.
Dynamic contrast ratio of a LCD can be improved by combination of LEDs as a backlight light source with a local dimming technique. LEDs are divided into a plurality of small sections to perform local dimming control. The local dimming technique is a technique enabling a backlight device to achieve different degrees of luminance and lighting variance in the different sections. Since LEDs have low power consumption and rapid switching speed, the same are suitable for application in local dimming technique.
However, because of point source characteristics of LEDs, light generated by LEDs is not directional light so that light entering a light guide plate is incomplete and uneven.
FIGS. 1 and 2 illustrate a conventional edge light backlight device including a light guide plate 7, a plurality of LEDs 8, a reflective plate (not shown) located underneath the light guide plate 7, and a prism sheet (not shown) located above the light guide plate 7. The light guide plate 7 has a light incident side 71 and a light emitting side 72. The light emitted by the LEDs 8 enters the light guide plate 7 through the light incident side 71 and undergoes reflection and refraction before emitting out of the light emitting side 72. A driving unit (not shown) is adapted to control the on/off modes of the LEDs 8 to perform local dimming. When a portion A of a screen needs to be bright and another portion B of the screen is otherwise dark, the driving unit controls the LEDs 8 near the portion A to be on and the LEDs 8 near the portion B to be off.
For a conventional backlight device, since there is no special structure to concentrate the light emitted from the light emitting side 72 of the light guide plate 7, light from the LEDs 8 near the portion A is likely to leak to the dark portion B, thereby causing halation and blurred motion image.